Camshaft for a variable-stroke exchange valve train

ABSTRACT

A camshaft of a sliding cam valve train in an internal combustion engine is provided. A cam piece ( 2 ), which has cam strokes of different lengths and can be displaced on a carrier shaft ( 1 ), is mounted on a rolling bearing at a camshaft bearing point ( 12 ) of the internal combustion engine. The outer race ( 16 ) of the rolling bearing ( 13 ) is formed by a one-piece bearing ring ( 17 ) which surrounds the cam piece and said race is smaller than a revolution radius of the longer stroke h 2.

BACKGROUND

The invention relates to a camshaft of a variable stroke gas exchangevalve train of an internal combustion engine. The camshaft comprises acarrier shaft and a cam part that is supported locked in rotation andaxially displaceable on the carrier shaft and has at least one first camgroup of at least two directly adjacent cams with different strokes andan axial connecting link in which an actuation element for shifting thecam part on the carrier shaft can be coupled, as well as a bearingjournal that runs between the first cam group and the axial connectinglink and on which a roller bearing supporting the cam part is held sothat it can rotate in a camshaft bearing point of the internalcombustion engine.

A gas exchange valve train which is also often called a sliding camvalve train with such a camshaft is known from DE 10 2009 030 373 A1.The cam parts supported with a central bearing journal between twointake or exhaust valves of an engine cylinder comprise two identicalcam groups each with three cams and an end-side axial connecting link inwhich two actuation pins for shifting the cam part into the three axialpositions can be coupled selectively. The publication alternativelyproposes a roller bearing for the cam part in addition to thehydrodynamic sliding bearing.

Despite the three-stage stroke variability, the known valve train has avery compact axial construction. This is achieved in that the camsadjacent to the bearing journals can dip into the camshaft bearing pointwhen they are not instantaneously active. A geometric requirement hereis a corresponding dimensioning of the rotational bearing, whosediameter must be greater than the surrounding circle of the camsentering within this circle. In the case of a roller bearing of the campart, this dimensioning would, however, lead to a camshaft bearing pointwith an undesirably large radial construction.

SUMMARY

The present invention is based on the objective of improving a camshaftof the type noted above such that, despite the roller bearing of the campart, it allows the most compact radial construction possible.

This objective is met in that the inner raceway of the roller bearing isformed by the bearing journal, the outer raceway of the roller bearingis formed by a one-part bearing ring, and the cam part and the bearingring have the following geometric properties:

a) h₁<h₂

b) max {r_(HK); r_(GK)+h₁}<r_(L)<r_(GK)+h₂

c) r_(L)<r_(AK)

Where:

h₁=Stroke of the cam adjacent to the bearing journal in the first camgroup

h₂=Stroke of the other cam of the first cam group

r_(HK)=Common enveloping circle radius of the cams of the first camgroup

r_(GK)=Base circle radius of the cams of the first cam group

r_(L)=Radius of the outer raceway

r_(AK)=Circumferential radius of the axial connecting link

These geometric relationships allow the radius r_(L) of the outerraceway to be less than the circumferential radius r_(GK)+h₂ of thelarge stroke h₂ but nevertheless the one-part bearing ring can bemounted on the bearing journal past the cams. The installation isperformed such that the bearing ring is first threaded into a positionon the cams eccentric to the rotational axis of the cam part and thencentered on the rolling bodies in the area of the bearing journal. Therolling bodies are advantageously held in a roller body cage that isopen on the periphery and is mounted on the bearing journal beforeinstallation of the bearing ring in the elastically expanded state.Alternatively, a multiple-part cage could also be used.

The invention could also be used in non-variable, roller-supportedstandard camshafts.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional features of the invention come from the following descriptionand drawings, in which the geometric relationships specified above areillustrated and explained in more detail using embodiments. If notmentioned otherwise, identical or functionally identical features orcomponents are provided with identical reference numbers. The hundredsplace of three digit reference numbers refers to the figure number.Shown are:

FIG. 1 a known variable stroke gas exchange valve train,

FIG. 2 a first embodiment of a cam part according to the invention inperspective view,

FIGS. 2 a-e the first cam part in different mounting positions of thebearing ring,

FIG. 3 the geometry of a cam part according to the invention inschematic view A according to FIG. 2,

FIG. 4 a second embodiment of a cam part according to the invention inperspective view,

FIGS. 4 a-f the second cam part from FIG. 4 in different mountingpositions of the bearing ring,

FIG. 5 a third embodiment of a cam part according to the invention inlongitudinal section,

FIG. 6 a fourth embodiment of a cam part according to the invention inlongitudinal section,

FIG. 7 a fifth embodiment of a cam part according to the invention inlongitudinal section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will be explained starting from FIG. 1, which shows athree-stage variable stroke gas exchange valve train of an internalcombustion engine. The basic functional principle of this known valvetrain can be summarized in that a conventionally rigid camshaft isreplaced by a camshaft with a carrier shaft 1 with external teethand—cam parts 102 arranged locked in rotation on this carriershaft—corresponding to the number of cylinders of the internalcombustion engine—and displaceable between three axial positions. Eachcam part has two identical groups of directly adjacent cams 103 to 105that have different strokes with identical reference circle radii. Thecam lift is performed by roller cam followers 6 that transfer the camtravels selectively to gas exchange valves 7.

The displacement of the cam part 102 required for operatingpoint-dependent activation of each cam 103, 104, or 105 on the carriershaft 1 is realized by a groove-shaped axial connecting link 108 inwhich, depending on the instantaneous axial position of the cam part,one of two pin-shaped actuation elements 9, 10 of an electromagneticactuator (not shown) is coupled, in order to displace the cam partwithin the common reference circle phase of the cam. To stabilize thecam part in the axial positions, a locking device is used that runs (notvisible here) in the interior of the carrier shaft 1 and locks in theinterior of the cam part.

For the radial support of the camshaft in the internal combustionengine, the cam part 102 is provided between the two cam groups with abearing journal 111 that is supported so that it can rotate in acamshaft bearing point 12 arranged locked in position and cylindricallycentered in the internal combustion engine. This is a split camshaftbearing point with a screwed-on bearing cover not shown here. Shown is ahydrodynamic sliding bearing of the bearing journal in the camshaftbearing point, wherein the bearing could also be formed in a known wayas a roller bearing.

FIG. 2 shows a first embodiment of a cam part 202 for a two-stagevariable stroke gas exchange valve, wherein the bearing journal 211 ofthe cam part is enclosed by a roller bearing 213 in a way according tothe invention. Differently than in the known cam part 102 in FIG. 1, thecam strokes of the first cam group arranged at a distance to the axialconnecting link 208 are oriented so that the stroke h₁ of the one cam203 adjacent to the bearing journal is smaller than the stroke h₂ of theother cam 204. For this first cam group, the following relationship isthen applicable:

a) h₁<h₂ (see also FIG. 3)

The cutaway and greatly simplified roller bearing 213 is a needlebearing with cage-supported needles 214, whose inner raceway 215 isformed by the bearing journal 211 and whose outer raceway 216 is formedby a one-part bearing ring 217 drawn onto the cam part 202. The plasticneedle cage 218 is shown as needle ring 19 below in connection with theneedles held therein, i.e., as 219 in FIG. 2. The width of the bearingring 217 is approximately twice as large as the length of the needles214 that roll, depending on the axial position of the cam part, eitherin one axial raceway half or in the other axial raceway half of thebearing ring mounted in the internal combustion engine.

FIG. 3 illustrates the geometric radii or diameter relationships on thecam part 202 (cam parts 402 to 702 accordingly) that are projectedaccording to view A in FIG. 2 in the plane of the sheet. The two cams203 and 204 have a common enveloping circle with radius r_(HK) thatencloses the same reference circle radius r_(GK) and the two differentstrokes h₁ and h₂ of this cam. In the shown case, however, the smallerstroke h₁ runs, with respect to its angular position, not completelywithin the larger stroke h₂, and the circumferential radius r_(GK)+h₁ ofthe cam 203 rotating about the camshaft axis 20 is greater than thecommon enveloping circle radius r_(HK). The smallest possible radiusr_(L) of the outer raceway 216 for the installation of the bearing ring217 is now generally the larger value of these two radii r_(GK)+h₁ andr_(HK), so that the following relationship is also applicable:

b1) max {r_(HK); r_(GK)+h₁}<r_(L)

On the other hand, in order to keep the radial installation space of thecam part 202 with the needle bearing 213 as small as possible, therelationship, according to which the outer raceway radius r_(L) issmaller than the revolution radius of the greater cam 204 about thecamshaft axis 20, is also applicable:

b2) r_(L)<r_(GK)+h₂

Example calculation for the outer raceway radius r_(L) for the camgeometry according to FIG. 3:

From

r_(GK): 15.0 mm

h₁: 6.4 mm

h₂: 11.3 mm

gives

r_(HK): 20.6 mm

r_(GK)+h₁: 21.4 mm

max {r_(HK); r_(GK)+h₁}=21.4 mm

r_(GK)+h₂: 26.3 mm

and the following size relationship is applicable for the outer racewayradius:

21.4 mm<r_(L)<26.3 mm

The drawing of the bearing ring 217 on the cam part 202 will beexplained with reference to FIGS. 2 a to 2 e.

FIG. 2 a: The needle ring 219 open on the periphery is expandedelastically in the radial direction and is snapped onto the bearingjournal 211 from the lateral direction. The width of the needle cage 218and the width of the bearing journal are essentially the same size, sothat the needle cage is supported directly in the axial direction fromthe facing end sides 221 and 222 of the inner cam 204 of the second camgroup and cam 203, respectively, adjacent to the bearing journal.

FIG. 2 b: The bearing ring 217 is threaded eccentric to the camshaftaxis 20 onto the outer cam 204. In this case, the smaller stroke h₁extends with respect to its angular position completely within thelarger stroke h₂, and the radius r_(L) of the outer raceway 216 isslightly greater than the common enveloping circle radius r_(HK) of thecam 203, 204 with r_(HK)=½ (2 r_(GK)+h₂). The drawn radius r_(AK)designates the outer circumferential radius of the axial connecting link208 and is also greater than the outer raceway radius r_(L):

c) r_(L)<r_(AK)

FIG. 2 c: The bearing ring 217 is pushed into the eccentric positionover the outer cams 203, 204 until the outer cam 204 is free.

FIG. 2 d: The bearing ring 217 is centered on the camshaft axis 20.

FIG. 2 e: The bearing ring 217 is pushed over the needles 214.

FIG. 4 shows a second embodiment of a cam part 402 according to theinvention. This differs from the previously explained cam part 202essentially by the axial support of the needle cage 418. Pulling thebearing ring 417 onto the cam part will be explained with reference toFIGS. 4 a to 4 f.

FIG. 4 a: The bearing ring 417 is threaded eccentric to the camshaftaxis 20 onto the outer cam 404 and pushed over the outer cams 403 and404 until the outer cam 404 is free. The needle ring 419 is pushedtoward the inner cam group to create an axial opening for the bearingring 417.

FIG. 4 b: The needle ring 419 and the bearing ring 417 centered relativeto the camshaft axis 20 are pushed one onto the other.

FIG. 4 c: A plastic spacer ring 423 that is open on the periphery isexpanded elastically in the radial direction and snapped onto thebearing journal 411 from the lateral direction.

FIG. 4 d: The spacer ring 423 is inserted into a ring groove 424 betweenthe inner raceway 415 and the inner cam 404 of the second cam group.

FIG. 4 e: The bearing ring 417 is displaced toward the inner cam 404until another ring groove 425 is freely accessible between the innerraceway 415 and the outer cam 403.

FIG. 4 f: As in FIG. 4 c, another spacer ring 423 is inserted into theother ring groove 425 so that the facing cam end sides 421 and 422support the needle cage 418 in the axial direction by means of thespacer rings 423.

FIG. 5 shows a third embodiment of a cam part 502 according to theinvention. In this case, the bearing journal 511 is formed with largesteps in the radial direction with a raised inner raceway 515, whereinboth end sides 526 and 527 of the radial step support the needle cage518 surrounding these sides in the axial direction.

FIG. 6 shows a fourth embodiment of a cam part 602 according to theinvention. In this fourth embodiment, the axial support of the needlecage 618 is formed from a combination of the support in the secondembodiment and the third embodiment: The axial support is realized onone side on the cam end side 621 by means of the spacer ring 623 and onthe other side directly on the end side 626 of the radial step.

FIG. 7 shows a fifth embodiment of a cam part 702 according to theinvention. This fifth embodiment is a variant of the fourth embodimentin the way that the spacer ring 723 is formed in one piece on the needlecage 718.

LIST OF REFERENCE NUMBERS

-   (without the hundreds place, which refers to the figure number)-   1 Carrier shaft-   2 Cam part-   3 Cam-   4 Cam-   5 Cam-   6 Roller cam follower-   7 Gas exchange valve-   8 Axial connecting link-   9 Actuation element-   10 Actuation element-   11 Bearing journal-   12 Camshaft bearing point-   13 Roller bearing/needle bearing-   14 Roller body/needle-   15 Inner raceway-   16 Outer raceway-   17 Bearing ring-   18 Roller bearing cage/needle cage-   19 Needle ring-   20 Camshaft axis-   21 Cam end side-   22 Cam end side-   23 Spacer ring-   24 Annular groove-   25 Additional annular groove-   26 End side of radial step-   27 End side of radial step

1. A camshaft of a variable stroke gas exchange valve train of aninternal combustion engine, comprising a carrier shaft and a cam partthat is supported locked in rotation and axially displaceable on thecarrier shaft and has at least one first cam group of at least twodirectly adjacent cams with different strokes (h1, h2) and an axialconnecting link in which an actuation element is couplable for shiftingthe cam part on the carrier shaft, and a bearing journal that runsbetween the first cam group and the axial connecting link and on which aroller bearing supporting the cam part is held so that for rotation at acamshaft bearing point of the internal combustion engine, an innerraceway of the roller bearing is formed by the bearing journal, an outerraceway of the roller bearing is formed by a one-part bearing ring, andthe cam part and the bearing ring have the following geometricproperties:a) h₁<h₂b) max {r_(HK); r_(GK)+h₁}<r_(L)<r_(GK)+h₂c) r_(L)<r_(AK) where h₁=the stroke of the cam adjacent to the bearingjournal in the first cam group, h₂=the stroke of the other cam of thefirst cam group, r_(HK)=a common enveloping circle radius of the cams ofthe first cam group, r_(GK)=a base circle radius of the cams of thefirst cam group, r_(L)=a radius of the outer raceway, and r_(AK)=acircumferential radius of the axial connecting link.
 2. The camshaftaccording to claim 1, wherein the roller bodies of the roller bearingare held in a roller bearing cage that is open on a periphery.
 3. Thecamshaft according to claim 2, wherein the bearing journal has a radialstep with a raised inner raceway, and at least one end sides of theradial step supports the roller bearing cage axially.
 4. The camshaftaccording to claim 2, wherein the cam part has a second cam group of atleast two directly adjacent cams with different strokes (h₁, h₂),wherein at least one end side facing each other of the cams adjacent tothe bearing journal in the cam groups supports the roller bearing cageaxially.
 5. The camshaft according to claim 4, wherein the cam end sidesdirectly support the roller bearing cage axially.
 6. The camshaftaccording to claim 4, wherein at least one of the cam end sides supportsthe roller bearing cage axially by a spacer ring that is open on aperiphery.